FlexBox - 3 Column Rows
HTML
<div class="flex-row-container">
<div class="flex-row-item">1</div>
<div class="flex-row-item">2</div>
<div class="flex-row-item">3</div>
<div class="flex-row-item">4</div>
<div class="flex-row-item">5</div>
<div class="flex-row-item">6</div>
<div class="flex-row-item">7</div>
<div class="flex-row-item">8</div>
<div class="flex-row-item">9</div>
</div>
CSS
.flex-row-container {
background: #aaa;
display: flex;
flex-wrap: wrap;
align-items: center;
justify-content: center;
}
.flex-row-container > .flex-row-item {
flex-grow: 1;
flex: 1 1 30%;
height: 100px;
}
.flex-row-item {
background-color: #fff4e6;
border: 1px solid #f76707;
text-align: center;
}